The "Shema" (שְׁמַע), found in Deuteronomy 6:4, states that "YHVH (יהוה) is one." This verse can be interpreted to contradict the doctrine of the Trinity, yet this doctrine is quite prominent in Christendom. How, then, is the doctrine of the Trinity reconciled with this verse? How can this verse be understood to be in harmony with the doctrine of the Trinity?

I think the question here is find, but would you mind taking a little more care in the wording to scope it in the context of "how does Christianity respond to this verse being used as a prooftext" ... so that this cannot be construed to be a truth question and dragged off track (and just to make the inevitable cleanup easier on moderators!).
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Caleb♦Jun 20 '13 at 21:10

Notice that YHVH of hosts is speaking, and YHVH of hosts states that "He sent me" (שְׁלָחַנִי). Who can send YHVH of hosts, the Almighty God? Surely no creature has the authority to send YHVH of hosts!

YHVH of hosts is still speaking in Zech. 2:9. He states that "YHVH of hosts sent me."

To reiterate, YHVH of hosts is speaking in Zech. 2:8. He states, "He sent me." We ask, "Who sends YHVH of hosts?" In Zech. 2:9, this is answered when YHVH of hosts, who is still speaking, states, "YHVH of hosts sent me."

Again, YHVH is speaking. He states that "many nations shall be joined to YHVH in that day," instead of saying that "many nations shall be joined to me in that day." By the speaker, who is YHVH, referring to YHVH in the third person, there appears to be a distinction between YHVH who is speaking and another YHVH to whom the nations shall be joined in that day. Now, it's not unheard of for YHVH to speak about Himself in the third person. However, the last clause confirms that there is more than one YHVH being mentioned in this verse. YHVH, who is speaking, states, "...and you shall know that YHVH of hosts sent me to you."

The Hebrew verb שְׁלָחַנִי ("he sent me") is reiterated in three verses:

Zechariah 2:8

For thus said YHVH of hosts, "After glory He sent me (שְׁלָחַנִי) to the nations who spoiled you, for he who touches you touches the apple of His eye.

Zechariah 2:9

For, behold, I shall shake my hand upon them, and they shall be a spoil to their servants, and you shall know that YHVH of hosts sent me (שְׁלָחַנִי).

Zechariah 2:11

And many nations shall be joined to YHVH in that day, and they shall be my people, and I will dwell in your midst, and you shall know that YHVH of hosts sent me (שְׁלָחַנִי) to you.

"And I shall dwell" (וְשָׁכַנְתִּי) is repeated in both verses. YHVH is the subject of the verb in both verses. Notice v. 11. YHVH states, "...and I shall dwell in your midst," and then the same YHVH states, "...and you shall know that YHVH of hosts sent me to you."

In conclusion, we have explicit confirmation in the Tanakh that Israel believed there was more than one person named "YHVH" (יהוה). This is later confirmed in the New Testament when the Son is revealed to Israel and dwells in their midst.

Exegesis of Deuteronomy 6:4 in Consideration of Zechariah 2:8-11

If there exist more than one person named YHVH, i.e. the Father and the Son (and the Holy Spirit), what does it mean when Deut. 6:4 states that "YHVH is one" (יְהוָה אֶחָד)? It is not enough to say "YHVH is one," but we must know, YHVH is one what? Certainly YHVH is not one "person," for that would contradict the doctrine of the Trinity, and of course, Zech. 2:8-11.

Upon much consideration of the Shema in its immediate context, I believe it should be translated as,

"Hear O' Israel! YHVH is our God, YHVH is the only one!"

Moshe is exhorting Israel to understand that:

YHVH is their God

YHVH is the only one (i.e., the only true God, and Israel's only God)

The Shema is thus an affirmation of the monotheistic faith of Israel. This is in contradistinction to the polytheism that Israel witnessed in Egypt by the Egyptians, as well as the nations surrounding Israel (cp. Deut. 6:14).

Can the Hebrew word אֶחָד (echad), which literally means the numeral one, be understood in this sense? I believe there is a basis for it. Wilhelm Gesenius indeed states that אֶחָד can mean "one only of its kind" (A Hebrew and English Lexicon of the Old Testament, p. 32). Gesenius cites a few examples, such as Job 23:13, Eze. 7:5, and Song of Songs 6:8.

My dove, my undefiled, is but one; she is the only one of her mother; she is the choice one of her that bore her. The daughters saw her, and called her happy; yea, the queens and the concubines, and they praised her.

אַחַת is the simply the feminine declension of אֶחָד. Obviously, the dove is not "the one of her mother," but rather, "the only one of her mother." Here we see that אֶחָד can be translated as "only one" with the actual noun being implied from the preceding context. In Song of Songs 6:8, it is the mother's only dove. In Deuteronomy 6:4, YHVH is Israel's only God.

Summary

In conclusion, since the Father and the Son are one in essence, and both the Father and the Son are God (John 1:1), then the Shema is consistent with the doctrine of the Trinity which states that there are three persons who are essentially God. Since the name of God is YHVH, then the name of each person of the Trinity is YHVH. The Son, YHVH, is Israel's God, just as the Father, YHVH, is Israel's God, and the Holy Spirit, YHVH, is Israel's God. Each person of the Trinity is co-equal and co-eternal in nature, so there is no distinction of essence, but rather, only of persons.

Insofar as the doctrine of the Trinity (paradoxically) affirms that God is both one God and three persons, there is no conflict. In other words, the Trinity affirms this tautologically---a "trinity" affirms one-ness and three-ness by definition.

The Hebrew word translated "one" in Deut. 6:4 is the same Hebrew word for "one" as in Genesis 2:24, in which the two shall become "one" flesh. So we have the idea that one can be made up of several, in this case, two.

Also in Numbers 13:23, it speaks of "one" cluster of grapes which the spies brought out of Canaan, again, with the idea of one composed of several.

So the One in Deuteronomy 6:4 allows the idea of God being made up of several persons in the godhead. From much research, we have seen that the number of persons in the godhead is three, Father, Son, and Holy Spirit.

I think you have to differentiate a statement from God (which is necessarily the truth,) from Catholic Dogma determined by Bishops of the Empire at Nicea in 325.

The Trinity in Unity is an idea of some of the Bishops in the Empire and was voted upon by 300 Bishops in 325 at Nicea (near Constantinople and the Emperor.) It was not accepted by all Bishops, six rejected it. Some 500 other Bishops did not even attend. The statement of Trinity was not regarded as the truth about God. It was "the best they could come up with," at that time to hold the various factions of the Church together. Bishops had to agree to it or lose their Diocese and pension. The Trinitarian statement was revised several times to correct ambiguities, and the changes caused a split in the catholic church, which is only now being healed (partially.)

The Trinitarian understanding is different between various Trinitarian churches, (the wording is also different - but that's not a major problem.) It is not possible to determine the truth from these statements, as God is truth alone.

So, you must accept what God has stated in His own words.

To be a Roman Catholic you must agree to accept the Trinity in Unity statement.
To be an Anglican Catholic you must agree to the Apostle's creed which is slightly different.
To be an Episcopalian you must agree to the Nicene-Constantinople creed, which is a variation of the Nicene Creed.
The Orthodox Greek have a slightly different understanding ("and the son" is missing.)
The Latter Day Saints use the Trinitarian phrase: Father, Son, and Holy Ghost, but rather than consider them to be personalities (or personages) as do the catholics, they consider them to be persons.

I would not use these differences in understanding between the various religious groups to suggest that one is the truth and the other wrong. Their understandings is particular to their rite of admission to the Church. It was never meant as a description of God.